Wireless Operators' Growing Pains

Looking at second-quarter U.S. wireless subscriber estimates for the Big Four carriers, an investor might never know anything was amiss.

Analysts expect strong overall net additions of postpaid subscribers for the big wireless carriers, which report results over the next two weeks. In the past, that has led to higher earnings and better margins. But in an era of heightened competition, sparked by T-Mobile US and reinforced by...